Apparatus and method for ascertaining optimum drying conditions



Aug. 25, 1964 W. H. HAMILTON ETAL APPARATUS AND METHOD FOR ASCERTAINING OPTIMUM DRYING CONDITIONS Filed July 18, 1961 80 34/LJJ 36 O m: f':"""

INVENTORS' WILLIAM H. HAMILTON BXMANUEL E. FUENTEVILLA 74 M ATTORNEY United States Patent 3,145,562 APPARATUS AND METHUD FUR ASCERTAG OPTIMUM BRYlNG (IGNDlTiUNS William H. Hamilton, Philadelphia, Pa, and Iarrnei E.

Fuentevilla, Haddonfield, NHL, assignors, by mesnc assignments, to Pennsalt Qhemicals Corporation, Philadelphia, Pan, a corporation of Pennsylvania Filed .iuly 18, 1961, Ser. No. 124,964 6 Claims. (Cl. 73-76) This invention relates to a drying apparatus, and more particularly to a testing control apparatus capable of ascertaining the optimum temperature and time which specimens should be disposed within a freeze or vacuum drying apparatus.

In a conventional freeze drying process, articles such as food are disposed in a frozen state within freeze drying equipment which withdraws the water from the article by sublimation of the ice in the articles. Such freeze dried articles may remain for substantial periods of time without refrigeration or deterioration and may be reconstituted without loss of flavor by merely adding water thereto.

Heretofore, the temperature, pressure and the time period for the freeze drying process have been based on empirical formulae. That is, the time period and temperature of the freeze drying cycle have been merely a calculated guess similar to the information given for baking a cake. In the baking of a cake, the cake is permitted to remain in an oven at a specific temperature for an estimated period of time. At the expiration of the estimated period of time, the cake is taken out of the oven and tested with a toothpick to determine whether or not it is done.

Thus, it will be seen that the information available heretofore is merely a calculated guess with a built-in safety factor to assure that the length of time that the articles are subjected to the freeze drying process is adequate. The present invention is directed to a testing apparatus capable of ascertaining with extreme accuracy the temperature, pressure and length of time required for the freeze drying of substantially any article. The same information may be ascertained for vacuum drying articles.

The testing apparatus of the present invention includes a testing chamber wherein specimens are sub jected to a freeze or vacuum drying process with a weight responsive means being provided to ascertain the weight loss of the specimens at a particular temperature and pressure. Recorder means are provided for permanently recording the temperature, pressure and weight change relative to the period of time to which the specimens have been subjected to the freeze or vacuum drying process. The weight responsive means and the tray are preferably thermally isolated within the chamber and the weight responsive means is convertible for use with specimens subjected to radiant heat or conducted heat.

It is an object of the present invention to provide a testing apparatus capable of ascertaining the minimum temperature, pressure and time period at which a particular specimen should be subjected to a freeze or vacuum drying process.

It is another object of the present invention to provide a novel testing apparatus having a convertible weight responsive means capable of ascertaining the weight loss of specimens subjected to radiant heat or conducted heat during a freeze or vacuum drying process.

It is still another object of the present invention to provide a novel testing apparatus capable of ascertaining and permanently recording the temperature, pressure and weight loss of specimens subjected to a freeze or vacuum drying process.

It is a still further object of the present invention to provide a novel testing apparatus having means for thermally isolating specimens and a weight responsive means with respect to a housing within which the weight responsive means and specimens are disposed while the specimens are being subjected to a freeze or vacuum drying process.

It is a still further object of the present invention to provide a novel apparatus for controlling the temperature to which articles are subjected in a battery of freeze or vacuum drying apparatus.

It is still a further object of the present invention to provide a novel method of ascertaining moisture content of a specimen and recording the same.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a front elevation view of the testing control apparatus of the present invention.

FIGURE 2 is a longitudinal sectional view of the testing control apparatus of the present invention taken along lines 2?.. a

FIGURE 3 is a transverse sectional view taken along lines 33 in FIGURE 1, with the tray and the lower heater plate being shown in phantom for clarity of i1- lustration.

FIGURE 4 is a schematic illustration of the apparatus in FIGURES 1-3 controlling a battery of drying ovens.

Referring to the drawing in detail, wherein like numorals indicate like elements, there is shown in FIGURE 1 the testing apparatus of the present invention designated generally as lit.

The testing apparatus Iii comprises a cylindrical housing 12. adapted to be supported on a floor or the like by a plurality of legs 14. The cylindrical housing 12 is provided with an integral rear wall 16 at one end and a removable Wall 18 at the other end thereof. The removable front wall 18 is preferably made from a transparent material such as Lucite. However, it will be understood that the front wall 18 may be made from glass, metal with a transparent partition, etc.

The periphery of the front wall 18 is removably secured to a radially directed flange on the housing 12 by means of a plurality of bolts 243. it will be appreciated by those skilled in the art that a variety of latching means may be utilized in place of the bolts 24 The periphery of the front Wall 18 is hermetically sealed with respect to the radially directed flange in the housing 12 in any convenient manner such as by providing an O-ring seal therebetween. The O-ring seal should be made from a high temperature resistant, readily deformable material. For example, the Q-ring may be made from polytetrafiuoroethylene which is commercially available and known as Teflon.

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The chamber within the housing 12 of the testing apparatus may be evacuated by means of the conduit 22 and a condenser (not shown) having its outlet port connected to a vacuum pump 24. The vacuum pump 24 may be any one of a plurality of commercially available vacuum pumps. It has been conventional heretofore to effect the freeze drying process while the specimens are undergoing freeze drying so that the moisture may be readily conveyed away from the specimens. While the freeze drying processes which have been proposed heretofore include subjecting the specimens to a vacuum, it is to be emphasized that the present invention may be utilized with recently developed processes which are not predicated upon the use of a vacuum.

A thermal insulating rod 26 is reciprocally disposed within a bore of a boss 30 on the housing 12. The rod 26 is hermetically sealed with respect to the boss 36 by means of the O-ring seal 28. The lowermost end of the rod 26 is connected to a link 27. The link 27 is pivotably connected to an actuator arm 32 intermediate the ends thereof. One end of the arm 32 is pivotably connected to the housing 12. The other end of the arm 32 is adjustably positionable with respect to removable pins 36 extending through aligned holes in the parallel arms of a LJ-shaped bracket 34 on the housin" 12. Thus, adjustment of the position of the arm 32 and the resultant supporting thereof by pins 36 enables the rod 26 to reciprocate with respect to the boss 3%).

The adjusting mechanism capable of adjusting the vertical disposition of the rod 26 is merely exemplary of a plurality of conventionally available devices. it will at once be apparent to those skilled in the art that any number of equivalent devices may be substituted therefor.

The rod 26 is preferably made from a thermally insulating material such as polytetrafiuoroethylene, polytetrafiuorochloroethylene, etc. The end of the rod 26 remote from the arm 32 is fixedly secured to a base plate 38 on a weight responsive scale 42. Due to the material of the rod 26, it will at once be apparent that the scale 42 is thermally isolated with respect to the housing 12.

The weighing platform for the scale 42 comprises a pinion plate 44 having a plurality of arms 46 extending radially therefrom as shown more clearly in FIGURE 3. While four such arms 46 are illustrated in FIGURE 3, it will be appreciated that a greater or lesser number of arms may be utilized. The ends of the arms as remote from the pinion plate 44 are provided with tray engaging fingers 48 which project upwardly from the plane of the arms 46 for a substantial distance as illustrated in FIG- URES 1 and 2.

A tray 50 having an outwardly directed rim 52 is disposed within the housing 12. The tray 50 is adapted to support specimens which are to be subjected to a freeze drying process. A heater plate is disposed within the housing 12 between the tray Stl and the pinion plate 44*.

The heater plate 54 is spaced from the tray 56 and the pinion plate as so that the specimens within the tray 50 will be heated by radiant heat. The tray 5% is supported in spaced relationship with respect to the heater plate 54 by the engagement between the tray fingers 48 and the tray rim 52. The plate 54 is hollow and. is provided with conduits through which a hot or cold liquid may be circulated by means of conduits 56 and 58. The conduits 56 and 58 extend through the housing 12 and may be pro vided with suitable control valves (not shown).

The heater plate 54 is supported in spaced relationship with respect to the tray Si) by means of a pair of flanges 69 and 6% extending from a L-shaped bracket 62 and flanges 66 and 66' extending from a L-shaped bracket 64. The brackets 62 and 64 are fixedly secured to the inner peripheral surface of the housing 12; in any convenient manner such as by welding. In order to thermally isolate the heater plate 54 with respect to the housing t2, the ends of the flanges 6-9, 6%, 66, and 66 are provided with a notch within which is disposed a thermally insulating material 69. Also. the conduits 56 and 58 are insulated with respect to the housing 12 at the point where said conduits extend through the housing 12.

The bracket s2. is provided with a pair of flanges 72 extending therefrom in the same manner as flanges 60 and 6d. The flanges 72 are disposed above the tray 50 and cooperate with a pair of flanges ill on the bracket 64 to support a second heater plate 68. The heater plate 68 is identical with the heater plate 54 and is provided with conduits 7d and '76 extending through the housing 12. The heater plate 68 is adapted to heat the specimens within the tray 59 by radiant heat. Thus, it will be seen that the specimens adapted to be disposed within the tray 50 will be subjected to radiant heat from above and below the tray 50.

A recorder 78 adapted to provide a permanent record of temperature versus time is supported on bracket 86 which in turn may be supported from one of the legs 14. The recorder 78 is preferably a commercially available recorder capable of providing a multiline graph. A thermocouple (not shown) is disposed within the tray 50 and connected to the recorder 78 by Wire 82 so that the temperature of the specimens may be permanently recorded. A thermocouple (not shown) is attached to the heater plate 5 and connected to recorder 78 by means of Wire 84 so that the temperature of the heater plate 54 may be permanently recorded. The wires 82 and 84 extend through an aperture in the housing 12 and are hermetically sealed with respect thereto.

A recorder 86 capable of permanently recording weight versus time is supported on a bracket 38 which may be fixedly secured to another one of the legs 14. The recorder 25 is connected to the scale 42 by means of wires 93 and 92. If desired, the recorder 36 may be dispensed with. However, the elimination of the recorder 86 requires a worker to periodically read the weight on the scale 42. by looking through the transparent front wall 18 and then plotting the reading against time. Since the use of a worker for reading scale 42 and plotting a graph introduces a possibility for error, the provision of a recorder such as recorder 86 is preferred.

A pressure gage $4 is connected to the housing 12 and a recorder 96 to permanently record pressure versus time.

The testing apparatus 10 is utilized in the following manner:

Access to the interior of the housing 12 is had by removing the front wall 18. The removable bolts 20 accommodate the removal of the front wall 18. Atray 50 of specimens in a frozen state is disposed within the housing 12.

In commercially available equipment, the heat supplied to the specimens undergoing a freeze drying process may be radiant heat or conducted heat. If the equipment to be utilized for the freeze drying process is of the radiant heat type, the tray 59 will be supported by the fingers 48 so as to be spaced from the heater plates 54 and 68. Thereafter, a thermocouple connected to recorder 78 by means of wire 32 will be disposed among the specimens within tray 5%. A thermocouple connected to the recorder 78 by means of wire 8 will be fixedly secured to the heater plate 54.

Thereafter, the front wall 13 will be fixedly secured to the housing 12 with a hermetic seal therebetween. The chamber within the housing 12 will then be evacuated by means of the vacuum pump 24 while a heating medium such as steam, hot water, or the like will be circulating through the heater plates 54 and 64. If desired, the heater plates 54 and 64 may be of an electrical type.

As the frozen specimens are subjected to heat and the vacuum within the chamber of the housing 12, the icewithin the specimens will sublime with the resultant vapor being carried away by the conduit 22 under the effect of the vacuum pump 24. As the ice within the specimens sublimes, the weight of the specimens will be reduced.

23 While the weight of the specimens is being reduced, the temperature of the specimens and the heater plate 54 are being permanently recorded by the recorder 78 while the change of weight is being recorded by the recorder 86 and the pressure is being recorded by the recorder 96.

As soon as the graph produced by the recorder 86 reaches a plateau, the freeze drying of the specimens has been completed. By varying the temperature of the heater plates 54 and 68 and the pressure in housing 12 and repeating the above process, the exact minimum temperature, pressure and period of time necessary for a particular specimen may be accurately ascertained by the use of the testing apparatus of the present invention.

It will be noted that the specimens as well as the heater plate 54 have been thermally isolated with respect to the housing 12 so as to increase the accuracy of the graph produced by the recorder 78. If the heat generated by the heater plates 54 and 68 is permitted to be conducted to the housing 12, the accuracy of the apparatus 10 will not correspond with the commercially available apparatus wherein the specimens and heater plates are thermally isolated from their respective housings.

If the commercial apparatus is of the type wherein the specimens are heated by conduction, the arm 32 will be manipulated so that the fingers 48 are disposed below and out or" contact with the rim 52 on the tray 50. At periodic intervals, the arm 32 will be manipulated so as to raise the fingers into abutting contact with the rim 52 on the tray 50 so that a reading may be produced and recorded by the recorder 86. The arm 32 is then manipulated so as to permit the tray 50 to descend and be supported by the heater plate 54. In this manner, the reading obtained will be that of the weight of the tray 50 and the specimens and will not include the weight of the heater plate 54.

In vacuum drying, the specimens are not frozen when placed into the housing 12. The present invention may be utilized to ascertain the variables set forth above.

Thus, it will be seen we have invented a novel testing apparatus capable of ascertaining with extreme accuracy the minimum time, pressure and temperature required for the freeze or vacuum drying of substantially any type of specimen. Also, the apparatus 10 of the present in vention is convertible so that the desired information may be obtained whether the specimens are heated by radiant heat or conducted heat. The information ascertained from the testing apparatus of the present invention eliminates the guesswork needed heretofore when freeze or vacuum drying various specimens.

The information attainable from the testing apparatus of the present invention enables a freeze or vacuum drying process to be accomplished with confidence that the process may be repeated a plurality of times While attaining uniformity in the freeze dried product so long as the type and size of the product remains substantially constant.

The apparatus 10 may be utilized as illustrated schematically in FIGURE 4 to control a battery of drying ovens. As illustrated, the apparatus 10 is connected to a temperature controller Hit). The controller 1% may be connected to the recorder 78. The controller 1% is capable of sending out a signal by wire N32 to the apparatus 10 as well as the ovens 14. 4, 1% and 1438.

The controller 100 will control the temperature to which the articles are being subjected in apparatus 10, and ovens 19 i, 106 and 198. In this manner, the articles will be subjected to only the maximum safe temperature consistant with food quality. In order to control the temperature to which the articles are subjected, the coutroiler 160 may, for example, control a valve in the conduits 56 and 74 of the apparatus 10 and comparable concluits for the ovens 194, 106 and 138. While only three such ovens are illustrated, it will be appreciated that a greater or lesser number may be provided.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. Testing apparatus comprising a housing having a chamber therein, a removable portion of said housing hermetically sealed thereto for providing access to said chamber, a tray thermally isolated from and supported within said chamber and adapted to contain specimens, means for vacuum drying specimens adapted to be disposed within said tray, said last-mentioned means including vacuum means for evacuating said housing and heating means for heating specimens contained within said tray, weight responsive means operatively associated with respect to and thermally isolated from said tray for ascertaining the weight of the specimens while they are being dried, means for indicating the temperature of said specimens while they are being dried, means for indicating the temperature of said heating means while the specimens are being dried, and means for indicating the pressure within said chamber while the specimens are being dried, whereby the optimum temperature, pressure and time period for drying substantially any type of specimen may be ascertained.

2. The testing apparatus of claim 1 including a battery of drying ovens, a temperature controller operatively disposed with respect to said housing and said battery of ovens, said temperature controller being controlled in accordance with said means for indicating the temperature of said heating means, said temperature controller controlling said battery of drying ovens in accordance with the temperature of said heating means, whereby said temperature controller regulates the temperature within said housing and said ovens so that specimens within said housing and said ovens are subjected only to the maximum safe temperature consistent with specimen quality during the drying thereof.

3. The testing apparatus of claim 1 wherein said heating means include conduction heating means in thermal conducting relation with said tray, said weight responsive means including a scale, and means for selectively interrupting said thermal conducting relation between said tray and said conduction heating means to connect said weight responsive means to said tray for periodic measurement of the Weight of said tray and specimens contained therein.

4. A method of ascertaining the optimum conditions for freeze drying of a specimen comprising the steps of placing a frozen specimen on a tray, placing the tray and specimen within a housing thermally isolated from the tray, hermetically sealing the housing, subjecting the specimen to heat sufficient to expel moisture therefrom while continuously subjecting the specimen to a vacuum, continuously measuring the weight and temperature of the specimen, continuously measuring the pressure within the housing, continuously measuring the heat supplied to the housing, and continuously recording the weight, temperature and pressure whereby a record may be obtained indicative of the optimum conditions for freeze drying the specimen on the tray.

5. The method of claim 4 including the steps of providing a second housing having trays and specimens therein similar to said first-mentioned housing, tray and speci mens, and controlling the conditions in said second housing in accordance with the measurements in the first housing to provide optimum conditions for freeze drying the specimens within the second housing.

6. Testing apparatus comprising a housing having a chamber therein, a removable portion of said housing hermetically sealed" thereto for providing access to said housing, a tray thermally isolated from and supported within said chamber and adapted to contain specimens,

means for vacuum drying specimens adapted to be disposed on said tray, said last-mentioned means including vacuum means for evacuating said housing and heating means for heating specimens on said tray, said heating means being below said tray, Weight responsive means operatively associated with respect to said tray and thermally isolated from said housing for ascertaining the Weight of specimens While they are being dried, and means for selectively moving said tray upwardly to canmeet said weight responsive means to said tray for periodic measurement of the Weight of said tray and specimens thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,709,914 Brabender et a1 June 7, 1955 2,907,117 Parkinson et a1 Oct. 6, 1959 3,074,270 Rabb Jan. 22, 1963 FOREIGN PATENTS 718,444 Great Britain Nov. 17, 1954 830,525 Great Britain Mar. 16, 1960 OTHER REFERENCES Publication: Thennograv, American Instrument Co., Inc., Silver Spring, Md, Bulletin 2328, March 1960, 8 pages. 

1. TESTING APPARATUS COMPRISING A HOUSING HAVING A CHAMBER THEREIN, A REMOVABLE PORTION OF SAID HOUSING HERMETICALLY SEALED THERETO FOR PROVIDING ACCESS TO SAID CHAMBER, A TRAY THERMALLY ISOLATED FROM AND SUPPORTED WITHIN SAID CHAMBER AND ADAPTED TO CONTAIN SPECIMENS, MEANS FOR VACUUM DRYING SPECIMENS ADAPTED TO BE DISPOSED WITHIN SAID TRAY, SAID LAST-MENTIONED MEANS INCLUDING VACUUM MEANS FOR EVACUATING SAID HOUSING AND HEATING MEANS FOR HEATING SPECIMENS CONTAINED WITHIN SAID TRAY, WEIGHT RESPONSIVE MEANS OPERATIVELY ASSOCIATED WITH RESPECT TO AND THERMALLY ISOLATED FROM SAID TRAY FOR ASCERTAINING THE WEIGHT OF THE SPECIMENS WHILE THEY ARE BEING DRIED, MEANS FOR INDICATING THE TEMPERATURE OF SAID SPECIMENS WHILE THEY ARE BEING DRIED, MEANS FOR INDICATING THE TEMPERATURE OF SAID HEATING MEANS WHILE THE SPECIMENS ARE BEING DRIED, AND MEANS FOR INDICATING THE PRESSURE WITHIN SAID CHAMBER WHILE THE SPECIMENS ARE BEING DRIED, WHEREBY THE OPTIMUM TEMPERATURE, PRESSURE AND TIME PERIOD FOR DRYING SUBSTANTIALLY ANY TYPE OF SPECIMEN MAY BE ASCERTAINED. 